It has long been known to enhance the comfort, convenience and utility of telescopes, binoculars and other such optical apparatus by providing these devices with an eyeguard to interface between the user's eye and the optical instrument. Eyeguards often take the form of a flexible rubber rim or cup extending from the eyepiece of the optical instrument. The eyeguard typically allows the user to comfortably position his eye against the instrument, assists the user in maintaining the proper eye relief distance, (i.e., the distance from the eye-end lens of the optical instrument to the user's eyeball) to provide the user with full field of view, and to shield the user's eye from ambient or reflected light, which may distract from the image transmitted through the optical instrument.
Enhanced vision devices comprise a class of optical, electro-optical and/or video instruments that employ light amplification, infrared or thermal imaging, video displays or other technologies to provide enhanced images and/information to the user. In some cases, enhanced vision devices allow the user to see under low-light or smoke-obscured conditions where conventional optical instruments would be ineffective. In other cases, enhanced vision devices provide sensor outputs (e.g., target range data) directly within the instrument's eyepiece. Examples of such enhanced vision devices include night vision goggles, starlight scopes, and thermal sights. Such devices find a wide range of applications including personnel-carried night vision goggles, weapon-mounted targeting scopes, and vehicle-mounted viewers and sights.
The use of enhanced vision devices at night or in other circumstances of darkness presents a problem for conventional eyeguards, especially when used under circumstances involving personal danger such as combat or law enforcement activities. It will be appreciated that, when an enhanced vision device is being used, light is emitted from the eyepiece. This emitted light primarily strikes the user's eye, and any excess light is blocked by the user's face pressing against the eyeguard as he looks through the instrument. However, when the user moves his eye back from the eyeguard, the emitted light continues projecting back from the end of the instrument, and may reflect from the user's face, clothing or surroundings. This “light leakage” may serve to disclose (i.e., to the enemy) the otherwise concealed position of the user. Conventional rim- or cup-type eyeguards provide little protection against “light leakage” from the eyepiece of an optical instrument; however, eyeguards having an automatic diaphragm that opens when the user's face presses against it and closes when the user's face is withdrawn, are known to address this problem. In particular, U.S. Pat. No. 5,623,367 to the current inventor discloses such an eyeguard with an automatic diaphragm. U.S. Pat. No. 5,623,367 is hereby incorporated by reference herein in its entirety.
For many optical devices, automatic eyeguards of the type disclosed in U.S. Pat. No. 5,623,367 serve to satisfactorily position the user's eye and prevent unwanted light leakage. However, such prior art automatic eyeguards may not be suitable for all devices because they tend to have a relatively small range of travel (i.e., in the eye-to-eyepiece direction) once the diaphragm is open, whereas some optical devices may require an eyeguard allowing a relatively long range of travel after the diaphragm is open. For example, some enhanced vision devices may require a range of travel between a first eye-to-lens distance optimal for a first purpose (e.g., good field of view) and a second eye-to-lens distance optimal for a second purpose (e.g., to read range data displayed in the eyepiece). A need exists, therefore, for an eyeguard having an automatic diaphragm that allows increased range of travel after the diaphragm is fully opened.